The present invention relates to a zoom mechanism for zoom lenses, and more particularly, to a zoom mechanism for zoom lenses which performs a zooming operation by moving a plurality of lens groups including a focusing lens group in their respective optical axis directions.
A lens shutter camera provided with a zoom lens generally comprises a zoom drive mechanism for driving each of the lens groups during the zooming operation and a focus drive mechanism for driving a focusing lens group during the focusing operation. In the prior art, however, in a mechanism for driving a focusing lens group, mechansims for zooming and focusing operations are provided in duplication. Accordingly, when an auto-focus apparatus is constructed with an electric motor driven zoom, its drive source (motor) doubles, resulting in an increase in size, number of parts and cost of a camera.
In addition, in a conventional zoom mechanism for zoom lenses, non-linear movement of a lens group is generally embodied by using a cam ring, cam member, non-circular gear or the like. In another case, a mechanism has been proposed in which after a zooming operation has been performed by moving a focusing lens group together with other lens groups in a unitary manner, a position of the focusing lens group is corrected during the focusing operation. With a cam ring, however, the cost and size of a camera increase. While a mechanism without a cam ring has also been proposed, such mechanism is complicated and the size of a camera cannot be made so small. In addition, while a proposal of reducing the number of cam members has been made, an amount of correction increases, resulting in a larger-sized camera body, complicated control and a reduced shutter release time.